In some cases, a metal oxide semiconductor (MOS) transistor is formed on a semiconductor substrate (epitaxial substrate) having an epitaxial layer or on a silicon-on-insulator (SOI) substrate.
For example, Japanese Unexamined Patent Application Publication No. 2013-222838 discloses a semiconductor device including a high-breakdown voltage MOS transistor and a CMOS transistor. An element formation region serving as a formation region of the high-breakdown voltage MOS transistor and the CMOS transistor is surrounded by isolation (deep trench isolation) formed in a deep trench.